Dig straight, shallow trenches, 2 to 3 feet apart, in prepared soil. Plant seed potatoes 12 inches apart and cover with about 3 inches of soil. When the shoots reach 10 to 12 inches tall, use a hoe or shovel to scoop soil from between rows and mound it against the plants, burying the stems halfway. Repeat as needed through the growing season to keep the tubers covered.
Cons: Yield may be limited by the quality of the soil. In places where the soil is badly compacted or low in organic matter, one of the aboveground techniques might work better.
Place seed potatoes on the surface of prepared soil, following the spacing specified for hilled rows, and cover them with 3 to 4 inches of loose, seed-free straw. Mound more straw around the stems as they grow, eventually creating a layer a foot or more in depth.
Pros: The thick mulch conserves soil moisture and smothers weeds. Harvest is effortless with no digging. This method is suggested as a way to thwart Colorado potato beetle.
Cons: Yield in the test plot was slightly less than in the hilled row. Field mice have been known to use the cover of straw to consume the crop.
3. Raised Bed
Loosen the soil in the bottom of a half-filled raised bed. Space seed potatoes about 12 inches apart in all directions and bury them 3 inches deep. As the potatoes grow, add more soil until the bed is filled. If possible, simplify harvest by removing the sides.
Pros: This method yielded the largest harvest in my trials, and the potatoes were uniformly large. Raised beds are a good choice where the garden soil is heavy and poorly drained.
Cons: The soil to fill the bed has to come from somewhere—and it takes a lot.
Commercial growing bags are constructed of heavy, dense polypropylene. Put a few inches of a soil-compost mixture in the bottom of a bag, then plant 3 or 4 seed potato pieces and cover with 3 inches of soil. Continue adding soil as the plants grow until the bag is filled. To harvest, turn the bag on its side and dump out the contents.
Pros: Grow Bags can be placed on patios or driveways or used where garden soil is of inferior quality. The bags should last for several growing seasons. Their dark color captured solar heat to speed early growth. Harvest was simple, and the yield was impressive, considering the small space each bag occupies.
Cons: This is a pricy technique. The brand of bag I used costs $12.95.
5. Garbage Bag
Plant a large plastic garbage bag following the instruction for a Grow Bag, punching a few holes through the plastic for drainage. Roll the top edge of the bag to help it stay upright; otherwise the bag is prone to sag and spill soil. To harvest, rip the bag and dump out the contents.
Pros: Like the Grow Bags, a garbage bag can be employed where in-ground growing is not an option. Black bags capture solar heat to speed early growth.
Cons: Aesthetically, this is the least appealing choice. Yield was meager, perhaps because the thin plastic allowed the soil to heat up too much, limiting tuber formation.
Following instructions found online at irisheyesgardenseeds.com, build a bottomless square box (I used lumber from discarded pallets). Plant the same as for a raised bed. The box is designed so additional slats can be screwed to the sides as the plants grow and soil is added. In theory, a bottom slat can be temporarily removed to facilitate the harvest of new potatoes. For the final harvest, tip the box and dump out its contents.
Pros: This is another raised strategy for growing potatoes where the garden soil is of poor quality. Yield was similar in quantity to that of a raised bed.
Cons: A lot of time and effort went into the construction of the box. I felt the results did not justify the effort.
Using hardware cloth with ¼-inch mesh, fashion a cylinder about 18 inches in diameter and 24 inches tall. Put several inches of soil in the bottom, then plant 3 or 4 seed potatoes and cover them with 3 inches of soil. Continue to add soil as the potatoes grow. To harvest, lift the cylinder and pull the soil back to expose the tubers.
Pros: In a climate with incessant spring rains, the wire mesh would provide excellent drainage and prevent the soil from becoming waterlogged. This is another raised technique to consider where garden soil is poor.
Cons: I harvested a limited number of undersized tubers from the cylinders—a dismal showing, probably because the soil-compost mixture I used dried out so quickly that the plants lacked adequate moisture.